----- Attempting Submission 2 (Tue Mar 20 13:12:39 GMT 2012) -----Confirming Ultra-cold (Teff < 500K) Brown Dwarf Suspects Identified with WISEDespite the spectacular success of wide-field, sky surveys (2MASS, SDSS, and UKIDSS) in uncovering a large population of brown dwarfs in the solar neighborhood, a gap of nearly 400 K remains between the coolest brown dwarfs known (Teff ~ 500 K) and Jupiter (Teff ~ 128 K). Yet it is exactly these cold, low-mass brown dwarfs that are essential to measuring the functional form of the low-mass mass function and determining the lower mass limit of star formation. With atmospheric conditions similar to those of giant planets, cold brown dwarfs are also excellent proxies with which to test the ultracool model atmospheres that are critical to our understanding of exoplanets. One of the primary science goals of the Wide-field Infrared Survey Explorer (WISE), a NASA mission that recently completed a survey of the entire sky at four mid-infrared wavelengths, is to discover a large population of these cool brown dwarfs. As part of a larger followup campaign that involves both ground- and space-based observatories, we were awarded 12 orbits in Cycle 18 (as part of a Cycle 7 Spitzer program) to obtain near-infrared WFC3 grism spectroscopy of twelve of our faintest and reddest, and thus presumably coldest, brown dwarf candidates. We here propose to obtain spectra of an additional four objects that, along with the twelve Cycle 18 targets, constitute the best cold brown dwarf candidates that we have identified in roughly half of the sky. These objects are too faint for spectroscopic verification from the ground so HST/WFC3 observations are the only avenue for confirming their ultracool nature.Proper spectral classification of T dwarfs requires spectra covering at least the 1.1−1.7 μm wavelength range (see Figure 4). We will therefore use the G141 grism in WFC3 which provides a resolving power of λ/∆λ ∼130 over the 1.1−1.7 μm wavelength range to observe 4 WISE brown dwarf candidates with J > 19.5. We will also obtain F125W imaging of each source in order to establish the wavelength zero-point of the spectra and set the absolute flux level of the resulting spectra.
Based on our previous experience with the spectral classification and modeling of late- type T dwarf spectra, we require a minimum S/N of 15 at the FWHM points of the J-band peak and a S/N of 20 for the direct images in order to absolutely flux calibrate the spectrum to 5%. We used the spectrum of the T8 standard 2MASS 0415−0935 and the WFC3 Exposure Time Calculator to estimate the exposure time required to reach the required S/N for each source. Including all overheads (guide star aquisition, instrument, dithers, and buffer dump) we can obtain the required S/N in a single orbit per object so in total we request 4 orbits. All observations will be dithered to aid with the removal of bad/hot pixels.COOL STARS12false0.00.0falsefalsefalsefalseSUPPORTEDSTARTJ2000J2000J=19.6STARTJ2000J2000J=19.5STARTJ2000J2000J=19.8STARTJ2000J2000WFC3/IRImagingNoNoF125WWFC3/IRSpectroscopicNoNoG141WFC3/IRImagingNoNoF125WWFC3/IRSpectroscopicNoNoG141WFC3/IRImagingNoNoF125WWFC3/IRSpectroscopicNoNoG141WFC3/IRImagingNoNoF125WWFC3/IRSpectroscopicNoNoG141POS-TARGDITHER0.572LINE0.365falsefalse74.653418.528WFC3-IR-DITHER-BOX-MIN1falseThe scheduling data was generated by CASM 20.0.CASM was run in Phase II mode./private/var/folders/n6/6j659z254pj_0v7fkjtm_0fc0000gn/T/OPVisit1373401942597687876.xmlWISE 0535-75002(Tic-Visit
:proposal-id 12544
:visit-id "01"
:proposal-version -1
:trans-version "20120125"
:date "20-Mar-2012 08:59:12.0"
:trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0
:FATAL-ERRORS 0 :CONTINUABLE-FATALS 0)
:number-of-orbits 1
:saa-model "30"
:si-bright-earth-limb-angle 20.0
:data-volume 1253424
:tdrss-contact-duration 0
:coron NIL
)
(Tic-Obset
:proposal-id 12544
:visit-id "01"
:obset-id "01"
:pcs-mode "FGS"
)
(Tic-Orbit
:proposal-id 12544
:visit-id "01"
:orbit-number 1
:pcs-time 333
:si-vis-utilization 3000
:al-overhead-at-end 0
:internal-dur-at-end 709
:dark-offset NIL
:dark-utilization 0
:max-dark-utilization 1920
:low-sky "N"
:pcs-visibility 3633
:pcs-gap 0
)true10The scheduling data was generated by CASM 20.0.CASM was run in Phase II mode./private/var/folders/n6/6j659z254pj_0v7fkjtm_0fc0000gn/T/OPVisit688686054786398196.xmlWISE 04102+15024(Tic-Visit
:proposal-id 12544
:visit-id "02"
:proposal-version -1
:trans-version "20120125"
:date "20-Mar-2012 09:12:18.0"
:trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0
:FATAL-ERRORS 0 :CONTINUABLE-FATALS 0)
:number-of-orbits 1
:saa-model "30"
:si-bright-earth-limb-angle 20.0
:data-volume 1183792
:tdrss-contact-duration 0
:coron NIL
)
(Tic-Obset
:proposal-id 12544
:visit-id "02"
:obset-id "02"
:pcs-mode "FGS"
)
(Tic-Orbit
:proposal-id 12544
:visit-id "02"
:orbit-number 1
:pcs-time 333
:si-vis-utilization 2800
:al-overhead-at-end 0
:internal-dur-at-end 500
:dark-offset NIL
:dark-utilization 0
:max-dark-utilization 1920
:low-sky "N"
:pcs-visibility 3249
:pcs-gap 0
)true10The scheduling data was generated by CASM 20.0.CASM was run in Phase II mode./private/var/folders/n6/6j659z254pj_0v7fkjtm_0fc0000gn/T/OPVisit1243466751994171000.xmlWISE 09430+36072(Tic-Visit
:proposal-id 12544
:visit-id "03"
:proposal-version -1
:trans-version "20120125"
:date "20-Mar-2012 08:57:06.0"
:trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0
:FATAL-ERRORS 0 :CONTINUABLE-FATALS 0)
:number-of-orbits 1
:saa-model "30"
:si-bright-earth-limb-angle 20.0
:data-volume 1253440
:tdrss-contact-duration 0
:coron NIL
)
(Tic-Obset
:proposal-id 12544
:visit-id "03"
:obset-id "03"
:pcs-mode "FGS"
)
(Tic-Orbit
:proposal-id 12544
:visit-id "03"
:orbit-number 1
:pcs-time 333
:si-vis-utilization 2900
:al-overhead-at-end 0
:internal-dur-at-end 500
:dark-offset NIL
:dark-utilization 0
:max-dark-utilization 1920
:low-sky "N"
:pcs-visibility 3301
:pcs-gap 0
)true10The scheduling data was generated by CASM 20.0.CASM was run in Phase II mode./private/var/folders/n6/6j659z254pj_0v7fkjtm_0fc0000gn/T/OPVisit9214070943353322918.xmlWISE 22094+27114(Tic-Visit
:proposal-id 12544
:visit-id "04"
:proposal-version -1
:trans-version "20120125"
:date "20-Mar-2012 08:55:42.0"
:trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0
:FATAL-ERRORS 0 :CONTINUABLE-FATALS 0)
:number-of-orbits 1
:saa-model "30"
:si-bright-earth-limb-angle 20.0
:data-volume 1183792
:tdrss-contact-duration 0
:coron NIL
)
(Tic-Obset
:proposal-id 12544
:visit-id "04"
:obset-id "04"
:pcs-mode "FGS"
)
(Tic-Orbit
:proposal-id 12544
:visit-id "04"
:orbit-number 1
:pcs-time 333
:si-vis-utilization 2800
:al-overhead-at-end 0
:internal-dur-at-end 500
:dark-offset NIL
:dark-utilization 0
:max-dark-utilization 1920
:low-sky "N"
:pcs-visibility 3257
:pcs-gap 0
)true10